The development of commercial economy brings generation of tremendous counterfeit and imitation of products of well-known brands in various fields, which causes severe economic losses and social problems and brings anti-counterfeit technology into wide demanding. The development of materials having optical-angle discoloration effect becomes rapid due to the advantageous of being recognized readily by publics, and the materials are widely used in the fields of anti-counterfeit and decorating materials.
The optical-angle discoloration effect of a material can be obtained through formation of an intermittent layered structure of the material. The effect can be seen from a thin film obtained by co-extrusion of a metal and ceramic sheet in alternative (Dobrowolski, J. A.; Ho, F. C. and Waldorf. A., Applied Optics, 1989, 28, p 14). However, the material has a high cost and cannot be used conveniently.
In addition, a cholesteric liquid crystal having selective reflection of light was used as optical security device previously, such as the technology disclosed in GB 1387398. However, the application of a small-molecular cholesteric liquid crystal is limited. Since the small-molecular cholesteric liquid crystal flows easily, they should be encapsulated, such as, sandwiched in a glass tank or formulated to microcapsules or other structures for application. U.S. Pat. No. 6,410,130 discloses coating a solution of a polymerizable cholesteric liquid crystal on a base film through a transfer roller, removing solvent through an oven tunnel, then UV curing the resultant to form a film having optical-angle discoloration, or grinding the resultant to produce pigment. However, one defect of the technology is that a pattern of optical-angle discoloration is obtained by printing with an oil ink made by adding the discoloration pigment obtained from the patent to a vehicle (or resin). The presence of the vehicle lowers the concentration of the discoloration pigment, and thus the discoloration effect is not very obvious and the color is not very colorful.